1. Field of the Invention
The present invention relates to prosthetic devices used for replacement of a natural joint and, more particularly, to prosthetic joints having reduced area bearing surfaces.
2. Background Information
It is known to provide prosthetic joints or joint assemblies for acetabulums, knees, ankles, shoulders, elbows, and wrists. Components of prosthetic joints such as that shown in U.S. Pat. No. 4,068,342 to Townley et al., provide a face having a continuous surface area of articulation for its corresponding member. While conventional prosthetic components beneficially provide a low-friction articular face for the surface of accompanying member, interaction between the articulating component and the member can produce joint debris. Such debris is expelled into the adjacent tissues and may cause adverse reactions in the surrounding bodily tissue.
Attempts have been made to prevent joint debris produced by prosthesis joint assemblies from entering surrounding bodily tissue. See for example, U.S. Pat. No. 4,731,088 to Collier, where a flexible enclosure is applied to a prosthetic joint to isolate the joint debris from the surrounding tissue. It is thus desirable to reduce wear associated with prosthesis joint assemblies.
Prosthesis joint assemblies may be fabricated from various materials. There are hard on hard bearing prosthetic joint assemblies and polyethylene on hard bearing prosthetic joint assemblies. Hard on hard bearing prosthetic joint assemblies or combinations are typically metal-metal or ceramic-ceramic. Polyethylene on hard bearing prosthetic joint assemblies or combinations are typically polyethylene-metal.
For hard-on-hard bearing combinations of an acetabular cup assembly, for example, a lower head to cup clearance (gap) results in lower wear. As well, smaller diameter implants have been associated with lower friction. As implant diameter (head and inner cup with respect to an acetabular cup assembly) increases, the same low clearance for a smaller diameter bearing combination results in a higher contact area for the larger bearing combinations. This results in a higher frictional torque and a reduction in the size of an inlet zone. Excessive reduction in the size of the inlet zone may reduce the potential for lubrication to occur. For polyethylene-on-hard bearing combinations, which have typically been smaller diameter implants, implant wear increases with implant diameter and decreasing clearance. The current trend, however, is towards larger diameter implants.
In view of the above and other considerations, it is an object of the subject invention to provide an improved prosthetic joint.
It is another object of the subject invention to provide an improved joint prosthesis having a surface that minimizes the production of joint debris which can result from articulating movement of the joint prosthesis post implantation.
Another object of the subject invention is to provide an improved prosthetic component of a joint prosthesis having a bearing surface that minimizes the production of joint debris which can result from articulating movement of the prosthetic component post implantation.
Still another object of the subject invention is to provide an improved prosthetic joint that has surfaces that maximizes lubricity in conjunction with a corresponding prosthetic component when implanted in a patient.
A further object of the subject invention is to provide a method of fabricating a prosthetic assembly that has an optimum contact or bearing area.
A still further object of the subject invention is to provide a method of fabricating a prosthetic assembly that has an optimum contact area for a range of prosthetic assembly sizes.
The subject invention is a prosthetic joint having a reduced area bearing surface, a method of determining the reduced area bearing surface for the prosthetic joint, and application of the determination of the reduced area bearing surface to a range of sizes of like prosthetic joints. Particularly, the subject invention is a prosthetic joint having interruptions in the bearing surface thereof that define the reduced area bearing surface, a method of determining an amount of interruptions (or of an amount of remaining bearing surface area) for the prosthetic joint, and the application thereof to a range of sizes of like prosthetic joints.
For hard-on-hard prosthetic bearing combinations and polyethylene-on-hard prosthetic bearing combinations, optimally designed interruptions in an articular face of one or both of the prosthetic bearing components provides a specific contact area or bearing surface that may be deemed xe2x80x9coptimum.xe2x80x9d This is achieved for a wide range of sizes of the particular prosthetic and/or prosthetic bearing component, while still maintaining the same low bearing component-to-bearing component clearance of the prosthetic assembly.
Optimally decreasing contact area in the articulating surface of one or both bearing components of the prosthetic assembly through interruptions in the surface thereof, provides benefits of larger diameter prosthetic components (with an associated increased range of motion, and decreased potential for dislocation), low frictional torques, and lower wear of smaller diameter prosthetic components.
In one form, the subject invention provides a bearing component for a prosthetic assembly. The bearing component includes a body having an articular surface. The articular surface has areas of relief that define an interrupted bearing surface. The areas of relief range from 0.3% to 83.2% relative to an otherwise uninterrupted bearing surface area, and from 0.01% to 31.88% relative to a total articular surface area.
In another form, the subject invention provides a bearing component for a prosthetic assembly. The bearing component includes a body defining an articular surface area. The articular surface area has a contact surface area defined by interruptions, wherein the interruptions range from 0.3% to 83.2% relative to an otherwise uninterrupted contact surface area, and from 0.01% to 31.88% relative to the articular surface area.
In another form, the subject invention provides a prosthetic joint assembly. The prosthetic joint assembly includes a first bearing component and a second bearing component. The first bearing component has an articular surface area adapted to receive the second bearing component. The articular surface area has a bearing surface area that is defined by interruptions, and is adapted to be contacted by the second bearing component. The interruptions range from 0.3% to 83.2% relative to an otherwise uninterrupted bearing surface area, and from 0.01% to 31.88% relative to the articular surface area.
In yet another form, the subject invention provides a method of making a bearing component for a prosthetic assembly. The method includes steps of: (a) forming a body having an articular surface; and (b) forming areas of relief in the articular surface to define an interrupted bearing surface wherein the areas of relief range from 0.3% to 83.2% relative to an otherwise uninterrupted bearing surface, and from 0.01% to 31.88% relative to a total articular surface area.
In still another form, the subject invention provides a method of making a bearing component for a prosthetic assembly. The method includes the steps of: (a) forming a body defining an articular surface area; and (b) forming the articular surface area with a contact surface area defined by interruptions wherein the interruptions range from 0.3% to 83.2% relative to an otherwise uninterrupted contact surface area, and from 0.01% to 31.88% relative to the articular surface area.
In a yet further form, the subject invention provides a method of making a prosthetic joint having a first body and a second body. The method includes the steps of: (a) determining a clearance distance between the first body and the second body; (b) determining a contact surface area value for the first and second body based on the clearance distance; and (c) forming the first body with interruptions in an articular surface thereof such that a bearing surface area defined by the interruptions in the articular surface equals the contact surface area value.
In another form, the subject invention provides a method of making a prosthetic assembly comprising a first body of a first material and a second body of a second material. The method includes the steps of: (a) determining a clearance distance between the first and second body; (b) deriving a baseline contact area value for the prosthetic assembly; and (c) providing interruptions in an articular surface of one of the first and second bodies based on the baseline contact area value, the interruptions providing an optimum contact area between the first and second bodies that is constant for a range of prosthetic assembly sizes.
The interruptions may be formed in only one prosthetic component or both prosthetic components (e.g. head and liner) of the prosthetic assembly/joint. Further, the interruptions may be formed macroscopically and/or microscopically.